I'm not sure what reasoning you're using, but it appears you aren't grasping the complexity of the argument.

For starters, Google search placement is a fundamental part of the search product, and is a wholly different product from Google Ads (which don't show up alongside search results). Search results and display ads aren't just different products--they're different markets (for example, print ads and tv ads are also advertising but are wholly separate forms of advertising from each other and from display ads and from search placement). So paying for placement in search results isn't an antitrust issue.

On the other hand, if buying search placement was contingent on also buying Google Ads, that would be a textbook example of antitrust abuse because Google's dominance in the search engine market is being used to leverage and interfere with the display ads market.